Preparation of gem-dinitroparaffins by electrolysis



Feb. 16, 1965 c. M. WRIGHT 3,169,913

PREPARATION OF GEM-DINITROPARAFFINS BY ELECTROLYSIS Filed May 10, 1961 POROUS ALUNDUM CUP SILVER GAUZE CATHODE PLATINUM WIRE BURIED IN SILVER POWDER BED ELECTROLYZED ANODE SOLUTION CONTAINING SALT I OF DINITROPARAFFIN AND I NITROPARAFFIN 2 Sheets-Sheet l XKIA'IIIJKIYXFAI COOLING JACKET COOLANT POROUS BED OF SILVER POWDER (ANODE) MEDIUM POROSITY FRIT (ANODE SUPPORT) RECEIVING FLASK RECYCLE ELECTROLYZED l SOLUTION SEPARATION SALT OF DINITROPARAFFIN FIG. I

CHARLES M. WRIGHT INVENTOR.

AGENT Feb. 16, 1965 C- M. WRIGHT PREPARATION OF GEM-DINITROPARAFFINS BY ELECTROLYSIS Filed May 10, 1961 2 Sheets-Sheet 2 NOISHBANOO WwPDZZz Om ON O rav u" mum Fzmm CHARLES M. WRIGHT I INVENTOR. BY M g m AGENT Unite States Patent 3,169,913 PREPARATION OF GEM-DINITROPAFFINS BY ELECTRULYSHS Charles M. Wright, Wilmington, Del, assignor to Hercules'Powder Company, Wilmington, DeL', a corporation of Delaware Filed May 10, 1961, Ser. No. 169,204 14 Claims. (Cl. 204-72) This invention relates to a method for the preparation of gem-dinitroparaflins and, more particularly, to an electrolytic method for the preparation of such compounds.

Electrolytic methods involving oxidative electrolysis ofnitro compounds have not been generally utilized. This to an extent has been due to the complex reaction mechanism which takes place atthe oxidative pole or anode and the uncertainty of behavior involved for obtaining end products. To a further extent, this has been due to the fact that known methods for the preparation of gem-dinitroparaffins, for example, by the electrolysis of aqueous alkaline solutions of primary nitroparafiins using a platinum or other inert anode, have been found deficient in respect to yields and current efilciencies.

Now, in accordance with the present invention,.an

I electrolytic method has been discovered in which the reaction mechanism involving oxidative electrolysis of nitroparafiins, although diificult to define, proceeds with a certainty of behavior to yield uniform products accompanied with high yields and current efficiencies. In this method an active silver anode is electrolytically oxidized in an aqueous alkaline solution of a nitroparaffin and nitrite ion. The oxidized silver reacts with the components of the solution to form the corresponding gem dinitroparafi-ln in solution and silver metal wherein the latter reprecipitates on the anode.

Thus, in the preparation of a salt of gem-dinitroparaffin by electrolysis in an electrolytic cell having a porous partition between its anode and cathode compartments, the present invention is concerned with a method which comprises passing an aqueous alkaline solution of mononitroparatiin and inorganic nitrite into the anode compertinent of the cell, said solutionbeing adjusted to-a pH of from about 9'to about 13, said mononitroparaffin containingfrorn 2 to 6 carbon atoms, and the anode being silver metal; subjecting-the solution to electrolysis at from about 20 to about 75 C. wherein the silver metal is electrolytically oxidized and reacts with the components of the solution to form dinitroparaffin in solution and the silver metal is reprecipitated at the anode; and.

separating the dinitroparafiin thus formed from the electrolyzed solution. In order to demonstrate the present invention, typical and preferred nitroparafiins were detail in the following examples.

EXAMPLE i I A solution'consisting of 6 grams of nitroethane, 9 grams of potassium nitrite in 100 ml. of water, adjusted to pH 10 by the addition of pellets of potassium hyutilized as described in droxide, was prepared in a l50-ml;beaker.' This was the 1 anode'soluti'on. 'A silver gauze anode'was inserted'in the beaker. ;The anode was constructed by forming a hat piece of ZO-mesh silver gauze, 6 x l5 cm., intoa cylinder. The edges were held together with silver solder and a platinum contact was soldered to the gauze at the point where the edges of the gauze were joined. A flat- 3,169,913 Patented Feb. 16, 195

assembly was mounted on a magnetic stirrer, the stirrer turned on, and the anode and cathode were connected to a direct-current power source. A constant current of 4 amperes was passed for 58 minutes. The temperature in the anode compartment increased from 25 C. to 40 C. during this period. The applied potential throughout the electrolysis was between 5 and 7 volts.

At the end-of the electrolysis the cathode compartment and the electrodes were removed, the anode was rinsed with a few ml. of hot water, the rinsings being added to the anode solution. The anode solution was warmed slightly -(to approximately 60 C.) to ensure that all of the potassium dinitroethane formed was in solution and filtered, with the aid of vacuum, through a medium porosity glass frit. The beaker and filter frit were Washed with a few ml. of hot water. Thisremoved some silver powder that had settled to the bottom of the beaker. The filtrate was cooled in-an ice bath to near 0 C. and

the potassium salt of dinitroethane crystallized as yellow 1.98 grams of potassium'Idinitroethane and 0.225 gra m of nitroethane in'sol'ution.

The total potassium dinitroethane producejd wasz' V 7 grams e 8.4.7X'.94=7. 96 (as crystals) plus insolution') Total 9.94

9.94 I 8 -00628 mole v v The amount of nitroethane present was 6.1 grams or rmrQ-tQQW? 1 Therefore 0.0 00 X TZW converted to product.

There was 0.225 gram ofnitroethane left after the electrolysis, or I 0.225

1 5 The moles of nitroethane consumed' aosoo-onoa oiofl The yield was The current efficiency was calculated as follows:

4 amps. 58 minutes X60 seconds=13,900 coulombs =0.144 equivalent X 100=87% current efficiency EXAMPLE 2 A solutioncontaining 6 grams of nitroethane, 6.5 grams of sodium nitrite in 100 ml. of water, adjusted to pH 10 by the addition of sodium hydroxide was prepared in a ISO-ml. beaker. This was the anode solution. The cell was set up exactly as in Example 1 using a new silver gauze anode. A constant current of 4 amperes (D.C.) was passed for 65 minutes; The temperature of the anode solution rose from 25 C. atthe start of the electrolysis to 42 C. at the end. The anode solution was filtered, the anode and the filter trit washed and the washing added to the anode solution as in Example 1. lnthis case, the sodium dinitroethane formed was soluble so no crystallization was carried out. The anode solution was analyzed polarographically' and found to contain 8.9 grams of .sodium dinitroethaneqand 019 gram of nitroethane.

By analogous calculations to these shown in Example 1, 78% of original nitroethane was converted to product, the yield was 80% and the current efficiency was 80%.

EXAMPLE 3 l An electrolytic cell was assembled as follows to demonstrate the feasibility of'continuou's operation; The anode compartment consisted of a jacketed, medium porosity, Pyrex glass Buchner funnel, 3 inches in diameter, having a capacity of about 150ml. 'Theanode was a porous bed ofpowdered silver metal.% inch deep which completely covered the filter: plateor anode support of the-funnel. Thepowdered silver metal had 'a particlesize, from 1 ni'itted passage of; .electrolyzed solution therethrough. Electrical contact for the anode: was a coil of platinum to 200 microns. whichrende'red' the bed porous, and perwire buriedin the silver powder bed. Thecathode coml partment was a flat-bottomed porous alundum cup of approximately 30 ml. capacity, supported-so thatits bottomwas /2 inch above the bed of silver. The cathode was a cylinder of silver gauze 30 SC1.'C111. in area." The cell is shown schematically in FIG. 1.

An anode'solution containing 30 grams of nitroethane,

grams of potassium nitrite, adjusted to :pH 11.5 with Y pellets of potassium hydroxide, was prepared in- 500 ml. of water. The anode compartment was filled with a portion of this solution that, had been preheated to C- The cathode'compartment .was, filled with'2% KOH as,

the cathode solution to the same liquid level asthe anode solution, A-constant current of 10 amperes, waspassed through the cell. During the electrolysis, the anode solution continuously. passedthrough'the bed of. silver metal and the: filter plate. -The .electrolyzed anode solution was collected'in a beakeror receiving flask.

set in an ice bath. Fresh anode solution, preheated to 60 C., wasconstantly added to the top of: the cell to keep the liquid level constant. Temperature of the anode-solution in the cell was maintained between 55". and 70 C. by cooling water, passing through the jacket. The applied-potential;wasapproximately 9 volts.

f The anode solution passed through the cell at a rate 350 The electrolysisfw'as carried out coritinu- .ously for 67m1nutes, interrupted only twice, momentarily,

ml. 'per hour.

to repla'cethe cathode solution with fresh 2% KQH. This was necessary-toprevent the build-up of very corlcentrated KQH in the cathode compartment.

7 At the end of 67 minutes, all of the fresh-anode solution had been added to the cell. The electrolysis was stopped. The cathode compartment was removed and the 1. The weight obtained was 21.74 grams. This material analyzed 96% pure potassium dinitroethane by the polarograph. The filtrate was made up to 500 ml. with distilled water. There had been a loss of approximately 50 ml. in volume during the above operations. This solution was analyzed and found to contain 6.2 grams of potassium dinitroethane and 14.4 gramsof nitroethane. This solution was made up to the original nitroethane, potassium nitrite concentration used for the first pass by adding 15.6grams of nitroethaneand 23 grams of potassium nitrite. The pH was adjusted to 11.5 With'pellets of potassium hydroxide. The solution was recycled and electrolyzed exactly as set forth for the first pass. The time of electrolysis was'69 minutes. i

The solid material crystallized from the. recycled solution after drying and weighing was found to weigh 27.10 grams. This material analyzed 94% potassium dinitroethane by the polarographs The recycle filtrate was analyzed and found to: contain 5.7 grams of potassium dinitroethane and 14.0 grams of nitroethane.

Polarograms of the above two solids and of the filtrate showed no evidence of silver. The yield and current efficiency were determined as follows:

Yield Total potassium dinitroethane produced:

grams 21.74X .96=20.9 27*.1OX 94 25.5 i 5.7 52.1

V Total nitroethane consumed31.6 grams 31.6 H a i mole 100 ='79% overall yield Current: efi'iciency v V 136 min. '60 seciX 1o amps.=71,,600 doulormbs 81,600; I t I -4285 equivalent 75? X 100 78 current efi'lciency EXAMPLE v4 An anode solution was preparedconta ining- 7.2 grams of l-nitropropane, 9 grams of potassium nitrite in v100 ml. of water, adjustedto pH 10. by .the addition of pellets of. potassiumhydroxide. The cellwas set upand' the electrolysis carried out exactly as in Example 1. The time ot electrolysis was, 60 minutes. at;4"a'mpe res. The. anode solution wa'sfiltered, cooled and crystalline product separated. This product. was washed with acetone, air! dried and placed in a dessicator. 1 The identity' of this product as the-potassium salt; of 1,1-dinitropropane was confirmed by C, H, N and K analyses, and by the occur between the pHs of '13 and 9. Above pH 13, no appreciable gem-dinitro compound is formed. pils less than 9, the nitroparafiins are only partially c'on- Cmumed for Potw verted to the aci-form. The efiect of pH on the reaction s u L apntrorgo Found (Percent) 5 is shown in FIG. 2 and Table I wherein nitroethane was pane men used to demonstrate this etlect. All runs shown in Table I were made exactly as Example 1, except that polar- 20. as 21. 14, 20. 7s v 293 2. 94' Z 97 ographic analysis was done directly on the anode solution 16-27 -84, 16116 with no separation of the crystalline potassium aci- 22.70 23. 29, 2a. 01

10 dinitroethane.

TABLE I g. of f Current 0 Nitro- Initial Yield Efii- P Run No. ethane, pH Electrode Current percent Oiency, sigr ifit Remarks 100 ml. percent EFFECT OF pH 0N REACTION 1 6 9 13. 85 Ag gauze90 4 amp-1 hr" 27 12. 5 pH 13.1 after min-all sq. cm. reaction occurred after S. 2 0 0 13.0 -000 do 75 43 g glgggg-jg-g- 3 0 a 11.0 -d0 d0 90 5s 52 {3% 3335;313:353; 4 e 9 10.5 do do s3 01 55 3% 2E Eli-jg? 5 0 9 9.0 .do d0 s5 71 72 {3% 3% filg-jfgs 6 9 9.4 -do d0 88 so 75- pH Elli cumin-11.0.

EFFECT OF NITRITE CONCENTRATE Ag gauze-90 pH at 30 I11ll1.-9.3. 7 0 9 10.0 mm m- 92 83 {pH at6Dmin.-12.1. s 0 13.5 10.0 d0 10 70 69 64 5% 3% fijfijlf 9 0 18 10.0 1 .-d0 70 73 0s {5% 333 33,

EXAMPLE 5 Furthermore, it has been determined that a molar Solutions were prepared and electrolysis carried out exactly as in Example 4, except that Z-nitropropan'e was used to demonstrate the results in using'a secondary nitroparafiin and the anode solution was electrolyzed for 30 minutes at 4 amperes. The electrolyzed; anode solution was placed in a separatory funnel and extracted with ml. of ether.

nitrogen. The residue was analyzed by infrared and found to contain 2,2-dinitropropa'ne. From the foregoing examples, it will be appreciated that electrolyticaly oxid zed silver can be used to prepare the aci-salt of gem-dinitroparaffins from the corresponding mononitro-parafiin and nitrite ion. The silver behaves essentially catalytically in the reaction as is most evident from Example 3 which showed no evidence'of silver consumption or lossf i The reaction can be carried out either with a silver gauze anode or an anode consisting of a bedof silver metal. With the silver gauze, deterioration does occur with prolonged use but it has been found, for example,

that at least 48 grams of potassium aci-1,1-dinitroethane can be produced with ananode containing 15 grams of silver. Thus, 0.14 mole of silver are consumed in the production of 0.39 mole of 1,1-dinitroethane. However, it should be emphasized that this is not a true silver consumption. The silver merelvleaves the gauze electrode surface and settles to the bottornas a firie powder. With the anode consisting of a bed of silver powder, the process can be carried out continuously and the unreacted starting niaterial can be recycled, as heretofore. demonstratedby Example 3 and schematically shown in 1. Also, it. has been found that the desired reaction Will The ether layer Wasseparated and the ether evaporated off on a steam bath under a stream of excess of from 30 to 156% nitrite ion can be used in accordance with -this'inventionas well as stoichiometric proportions, but that as the higher nitrite concentrations 45 are approached, reduced yields and current efii'ciency result. This is shown also in Tablel wherein 'nitroethaue Was used to'demonstrate'this eliect.

Still further, concentrations of the nitro'paraliins within 50.12%, and witha corr'esponding'increase in nitrite and time of electrolysis, yields and current efficiencies cornparable to thoseset forth for Example 1 are obtainable.

it will be notedjthat maximum current density was not obtained in respect to the silver bed anode since its true anode area was difii alt-to obtain as'will be the case with powdered or particulate beds. Nevertheless, in Example. 3 it Was demonstrated that 10 amperes otc'urrent when passedusing'a bed of overall area of approximately 10 sq. in. gave a current elliciency of 78%, and tor'con- 6p tinuous operation this may be further controlled and'adjnsted to approach the maximum effect. When silver in powdered or particulate form is utilized as the anode bed, it 'shouldhave a particle size of from about 1 to about 500 microns. I Y I 1 Moreover, the electrolysis of nitroparahins in accordance "with this invention should be carried out ata temperature of from about 20 to about 75 C.,' and prefer ablyin a vessel iaclreted for coolingsince the electrolysis reaction ge era't-es heat; At temperatures in the order of i C. and above, undue decompo'sitiodo'f the ga ndinitroparafiin product formed by the electrolysis occurs. The cathode in respect to the present invention serves the ordinary. funcnion of a cathode 'inan electrolytic cell. The use of an identical alkali metal for the anode and ,75 eathodesolutionsis merely a matter of convenience.

With

the purview 05 this 'inventionrnay run at least as high as However, some-advantage is obtained when using the same strong alkali metal for the anolyte and catholyte since the catholyte by diffusion through the porous partition tends to fortify the reactive anolyte as the electrolysis proceeds. Solutions ofother electrolytes may be employed as catholytes and the cathode may be an inert metal such as platinum or it may be silver which is only active from the viewpoint of reaction when used asthe anode. It is essential, however, that silverbe employed as the anode since it is electrolytically oxidized silver that reacts with the components of the anode solution to form the corresponding salt of dinitroparafiin. Thus, it is quite preferable to use either potassium or sodium consistently as the alkali metal for the anolyte, catholyte and source of inorganic nitrite ion. Generally, an electric current at a density of from about 0.02 to about 0.20 ampere per square centimeter of active electrode surface will be found adequate for effecting the electrolysis in accordance with this invention. However, when utilizing gauze electrodes such as set forth for Examples 1 and '2, it is quite preferaable that low current densities be used.

' The mononitroparafiins which may be utilized for this reaction include primary and secondary nitropar afdns containing from 2 to 6 carbon atoms. The first member of the panafiin series, nitromethane, does not react to produce a gem-dinitro compound. which may be utilized include nitroethane, l-nitropropane, l-nit-robutane, l-nitropentane, l-nitrohexane, Z-nitropro- Thus, the mononitroparafiins Y the electrolytic method of this invention can be conducted to give high yields of the desired products and at high current efficiencies. As the examples have demonstrated,

yields of at least 79% and current efiiciencies of at least;

78% have been obtained.

In view of the foregoing, it will be evident that this invention may be carried out by the use of various modifications and changes without departing from its spirit and scope, with only such limitations placed thereon as are imposedby the appended claims.

What I claim and desire to protect by Letters Patent isf 1. In the preparation of gem-dinitroparaflin by electrolysis in an electrolytic cell having a porous partition between its anode and cathode compartments, the methodv .whrchcomprises passing an aqueous alkaline solutionof mononitroparafiin and inorganic nitrite into the anode compartment of the cell, said solution being adjusted to a pH between 9 and 13, said mononitroparaffincontaining pane, Z-nitrobutane, 2-nitro-1-propanol, l-nitro-Z-propanol and Z-nitro 1,3-propanediol, with the only, known requirement being that the compound form a stable, soluble acisalt in aqueous alkali. The products obtained from the electrolysis in accordance with this invention, when a salt of gem-dinitroparaflin, may be separated from the electrolyzed anode solution by conventional procedures. a For example, the preferred method of separating the potassium salt is crystallization in a cooling bath followed by filtering. The sodium salt also may be separated in thismanner but this is' most elfectively accomplished on very concentrated solutions. The preferred procedure for separating the gem-dinitroparafiin from the salt is by acidification followed by ether extraction. l-lowever, itwill .be appreciated that in the utilization of a secondary nitroparafiin, the product obtained is not a salt butis the gem-dinitro paraffin itself which may be separated from theelectro- Iyzed anode solution by extraction followed by distillation.

Although it is not intended 'that the invention shall be limited to any particular theory of operation, the reactions that appear to take place may be writtenas follows wherein nitroethane, arpreferred material, is used as'an example; Cathode Reaction 'Anode reaction 2Ag- +2Ag++2e Theoxidized silver, either as free silver-ion or as an insoluble silver compound, reacts as follows:

' propane, 'LI-dinitrobutane, 1,l-dinitropentane, .Ll-dinitrohexane, 1,1-dinitro-2 pr0p anol,:2,-2 dinitropropane,

2,2-din-itrobutane, 2,2-dinitro l-propanol and 2,2-dinitr'o- 1,3-propanediol.- Y a The aforementioned compounds are valuable interme- 'diatesin chemicalsynthesis and more recently, particularfrom 2. to ,6 carbon atoms, and the anode being silver metal; subjecting the solution to electrolysis at from about cally oxidized and reacts with the components of the solution to form dinitroparaflin in solution'and the silver metal is reprecipitated at the anode; and separating the;

dinitr-oparafiin thus formed from the electrolyzed solution. 2. In the preparation of gem dinitroparafl n by electroly sis'in an electrolytic cell having -a porous partition between its anode andcathode compartments,the method which comprises passing an aqueous solution of mono-. nitroparafiin and alkali metal nitrite into the anode compartment of the cell, said solution beingadjusted to a pH between '9 and 13 by the addition of alkali metal hydroxide and the anode being silver metal; subjecting the solution to electrolysis at from about 20 to about 75 C. wherein the silver metal is electrolytically oxidized and reacts with the components of the'solution to form dinitroparaffin in solution and the, silver metal is reprecipitated at the anode; and separating the dinitrop-ar'aifin thus formed from the electrolyzed solution. 7 a

3. The method of claim 2 wherein the mononitroparafiin 1s a prnnary nitroparafiin. i

" 4. Themethod of claim 2 wherein the mononitroparaflin 1s a secondary nitroparaffin. V

5. The method of claim 2 wherein the mononitroparaflln is nitroethane.

,6. The method of claim .2 wherein the mononitroparafiin is l-nitropropane.

'7. The method of claim-2 wherein the mononitroparaffin is l-nitrobutane.

. 8. The method of claim 2 wherein the mononitroparafiin is Z-nitropropane.

9. The method of claim 2 wherein themononitroparatiin,

is 2 -nitrobutane.

10." The method of claim 2 wherein the mononitroparafiinis 2-nitro-1-propanol.

' 11; The, method of claim 2.wherein the alkali metal is potassium;

. 12. Themethod or claim 2 wherein the alkali metal is 13. The method of cl aim-2 wherein the anode is porous .1

silver metal powder. 14. The method ofclaim 2 wherein the anode is porous: silver metal powder and the'electrolyzed solution is recycled after separation-ofdinitroparafiin for make-up of F the said aqueous solution of mononitroparaflin and alkali OTHER REFERENCES metal ni trite. Plummer et a1.: Journal of American Chemical Society, References Cited by the Examm' er May 1954 pages 2720 7 UNITED STATES PATENTS 5 WINSTON A. DOUGLAS, Primary Examiner. 1,218,584 3/17 Sanders 204292 JOSEPH REBOLD, MURRAY TILLMAN, Examiners. 2,485,803 10/49 Bahner 204-79 2,583,048 1/52 Hannum et a1 260644 

2. IN THE PREPARATION OF GEM-DINITROPARAFFIN BY ELECTROLYSIS IN AN ELECTROLTIC CELL HAVING A POROUS PARTITION BETWEEN ITS ANODE AND CATHODE COMPARTMENTS, THE METHOD WHICH COMPRISES PASSING AN AQUEOUS SOLUTIN OF MONONITROPARAFFIN AND ALKALI METAL NITRITE INTO THE ANODE COMPARTMENT OF THE CELL, SAID SOLSUTION BEING ADJUSTED TO A PH BETWEEN 9 AND 13 BY THE ADDITION OF ALKALI METAL HYDROXIDE AND THE ANODE BEING SILVER METAL; SUBJECTING 